Regenerator and cryogenic refrigerator having regenerator

ABSTRACT

In a second displacer (33), a final layer (33c) measuring 10 K or lower in temperature is filled with spherical particles (34) of HoCu 2  which exhibit a specific heat greater than that of Er 3  Ni. An intermediate layer (33d) of 10 K to 15 K is filled with spherical particles (35) of Er 3  Ni, Er 3  Co or Nd. Further, an initial layer (33e) of 15 K or higher is filled with spherical particles (36) of Pb. By the use of such regenerative materials that exhibit the highest specific heats respectively for the individual temperature regions of 10 K or lower, 10-15 K, and 15 K or higher, the second displacer (33) exhibits an enhanced refrigerating capacity, as compared with the case of filling the final layer with the spherical particles of Er 3  Ni as conventionally done. This further makes it possible to construct the second displacer (33) in a compact size and in a reduced weight.

TECHNICAL FIELD

The present invention relates to a regenerator for keeping cryogenictemperatures obtained by iterating the introduction and expansion ofhigh-pressure refrigerant gas, and a cryorefrigerator having such aregenerator.

BACKGROUND ART

An example of the cryorefrigerator for obtaining cryogenic temperaturesby iterating the introduction and expansion of high-pressure refrigerantgas is shown in FIG. 6. A regenerator of this cryorefrigerator employs amagnetic regenerative material such as Er₃ Ni.

FIG. 6 is a sectional view of the cryorefrigerator. Thiscryorefrigerator is provided with a first displacer 3 which has a firstchamber with a regenerative material accommodated therein and which issealed in a first cylinder 1, and a second displacer 7 which has asecond chamber communicating with the first chamber and accommodating aregenerative material and which is sealed in a second cylinder 5. Thefirst chamber of the first displacer 3 is optionally communicated with ahigh-pressure chamber 12 having an inlet 11 or with a low-pressurechamber 14 having an outlet 13, via a valve stem 9 and a valve 10.

The communication path from the first chamber to the high-pressurechamber 12 or the low-pressure chamber 14 is switched over by rotatingthe valve 10 by means of a synchronous motor 15.

The cryorefrigerator having the above construction operates as follows.

Referring again to FIG. 6, a high-pressure refrigerant gas fed from acompressor (not shown) or the like is introduced into the first chamberof the first displacer 3 through the inlet 11 and via the valve 10 andthe valve stem 9, where the refrigerant gas undergoes heat exchange withthe regenerative material within the first chamber, thus being cooled(first stage). The refrigerant gas cooled in this way is then introducedinto the second chamber within the second displacer 7, where therefrigerant gas undergoes heat exchange with the regenerative materialwithin the second chamber, thus being further cooled (second stage).

After these processes, the valve 10 is rotated by the synchronous motor15, so that the first chamber is communicated with the low-pressurechamber 14. Then, the high-pressure refrigerant gas that has beenintroduced in the first chamber and the second chamber is quicklyexpanded, resulting in decrease in gas temperature. In this way, heatenergy obtained by the expansion of the refrigerant gas is accumulatedon the regenerative material.

As described above, a cryogenic temperature is obtained by iterating theintroduction of the high-pressure refrigerant gas into the first chamberand the second chamber and its expansion (i.e., by iterating therefrigerating cycle).

In the cryorefrigerator having a structure as shown in FIG. 6,typically, spherical particles 16 of lead (Pb) are filled as aregenerative material on the high-temperature side of the second chamber6, while spherical particles 17 of Er₃ Ni are filled on thelow-temperature side of the chamber, as shown in FIG. 7, in order toenhance the low temperature regenerative efficiency in the seconddisplacer 7.

In the conventional cryorefrigerator, high regeneration efficiency hasbeen obtained by filling the spherical particles 16 of Pb on thehigh-temperature side of the second chamber 6 and filling the sphericalparticles 17 of Er₃ Ni on the low-temperature side of the chamber asdescribed above.

In recent years, such a cryorefrigerator as described above has come tobe applied in an increasingly wider range. With this trend, there aredemands for a cryorefrigerator having an even larger refrigeratingcapacity and being small in size and light in weight.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a regenerator havinghigh refrigerating capacity and also to provide a lightweight,small-sized cryorefrigerator having a regenerator of such a highrefrigerating capacity.

In order to achieve the above object, according to the presentinvention, there is provided a regenerator comprising:

a final layer which is filled with a regenerative material having HoCu₂and which forms a temperature region of 10 K or lower; and

a high temperature layer which is filled with a regenerative materialexhibiting a specific heat greater than that of HoCu₂ at temperatureshigher than 10 K and which forms a temperature region of higher than 10K.

The final layer of the regenerator is filled with the regenerativematerial having HoCu₂ that exhibits a specific heat greater than that ofEr₃ Ni in the temperature region of 10 K or lower. On the other hand,the high temperature layer is filled with the regenerative material thatexhibits a specific heat greater than that of HoCu₂ in the temperatureregion of higher than 10 K. By thus filling the regenerative materialsthat exhibit the greatest specific heats for the individual temperatureranges, respectively, the refrigerating capacity of the regenerator isenhanced.

In one embodiment, the high temperature layer has an initial layer whichmakes a high temperature region and an intermediate layer which makes alow temperature region. The initial layer is filled with a regenerativematerial including Pb or an alloy of Pb. The intermediate layer isfilled with a regenerative material which exhibits a specific heatgreater than that of HoCu₂ and lower than that of Pb in a temperaturerange corresponding to the intermediate layer.

With this arrangement, the refrigerating capacity of the regenerator isfurther enhanced because the high temperature region that exhibitstemperatures higher than 10 K is divided into the initial layer and theintermediate layer, and each of these layers is filled with aregenerative material that exhibits the highest specific heat for itscorresponding temperature range.

Also, in one embodiment, the intermediate layer of the high temperaturelayer is filled with a mixture of a plurality of regenerative materialswhich each exhibit a specific heat greater than that of HoCu₂ and lowerthan that of Pb in a temperature range corresponding to the intermediatelayer.

According to this arrangement, the intermediate layer is filled with amixture of a plurality of regenerative materials exhibiting a specificheat higher than that of HoCu₂ filled in the final layer and lower thanthat of Pb filled in the initial layer. Therefore, possible temperaturefluctuations during the refrigerating cycle are absorbed.

Also, in one embodiment, the intermediate layer of the high temperaturelayer is filled with Er₃ Ni, Er₃ Co or Nd.

In this arrangement, in the intermediate layer, Er₃ Ni, Er₃ Co or Nd isfilled as the regenerative material that exhibits a specific heatgreater than that of HoCu₂ and lower than that of Pb in the temperaturerange corresponding to this intermediate layer. Thus, the refrigeratingcapacity of the intermediate layer is enhanced.

In one embodiment, in the intermediate layer of the high temperaturelayer is filled with a mixture of Pb and Er₃ Ni or a mixture of Pb andEr₃ Co.

In this arrangement, in the intermediate layer, either the mixture of Pband Er₃ Ni or the mixture of Pb and Er₃ Co is filled as the mixture of aplurality of regenerative materials exhibiting a specific heat greaterthan that of HoCu₂ and lower than that of Pb filled in the initial layerin a temperature range corresponding to this intermediate layer.Therefore, when a high temperature end portion is at a temperature of ashigh as 40 K, possible temperature fluctuations of the intermediatelayer during the refrigerating cycle are effectively absorbed.

In one embodiment, the intermediate layer constituting part of the hightemperature layer is filled with a mixture of Er₃ Co or Ho₂ Al, and anyone of Er₃ Ni, HoCu₂, ErNi, and ErNiCo.

In this arrangement, in the intermediate layer, a mixture of either Er₃Co or Ho₂ Al and any one of Er₃ Ni, HoCu₂, ErNi or ErNiCo is filled asthe mixture of a plurality of regenerative materials exhibiting aspecific heat greater than that of HoCu₂ and lower than that of Pbfilled in the initial layer. Therefore, when the high temperature endportion is at a temperature of 20-40 K, temperature fluctuations thatwould occur in the intermediate layer during the refrigerating cycle areeffectively absorbed.

Further, according to the present invention, there is provided acryorefrigerator which has a first displacer inserted in a firstcylinder and accommodating a regenerative material within a firstchamber, and a second displacer inserted in a second cylinder andaccommodating a regenerative material within a second chamber, whereinthe first displacer is connected to the second displacer with the firstchamber being communicated with the second chamber, and a refrigerantgas is introduced from the first chamber to the second chamber so thatheat exchange between the refrigerant gas and the regenerative materialsof the first and second chambers is carried out, characterized in that:

the second chamber comprises three layers of a final layer which forms atemperature region of 10 K or lower, an intermediate layer which forms atemperature region of higher than 10 K and not higher than a specifiedtemperature, and an initial layer which is at a temperature higher thanthe specified temperature;

the final layer is filled with HoCu₂ as a regenerative material;

the intermediate layer is filled with Er₃ Ni as a regenerative material;and

the initial layer is filled with Pb as a regenerative material.

With this arrangement, in the initial, intermediate and final layers ofthe second chamber, regeneration at low temperatures is effectedefficiently by the regenerative materials that exhibit the highestspecific heats for the temperature regions of the individual layers,respectively, so that the refrigerating capacity of the second chamberis enhanced. Accordingly, the amount of such regenerative material to beloaded can be reduced, which enables the cryorefrigerator to be mademore lightweight and compact.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration showing an example of a regenerative materialfilling structure in the regenerator of the present invention;

FIG. 2 is a graph showing the specific heat characteristics of variousregenerative materials in a cryogenic temperature range;

FIG. 3 is an explanatory diagram of temperature fluctuations that occurin the intermediate layer during the refrigerating cycle;

FIG. 4 is an illustration showing a regenerative material fillingstructure different from that of FIG. 1;

FIG. 5 is an illustration showing a regenerative material fillingstructure different from those of FIGS. 1 and 4;

FIG. 6 is an illustration of an example of the cryorefrigerator in whichthe regenerator of the present invention is used; and

FIG. 7 is an illustration showing the regenerative material fillingstructure of the prior art.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 illustrates a regenerative material filling structure in aregenerator according to one embodiment of the present invention. In asecond displacer 33 sealed in a second cylinder 32 communicating with afirst cylinder 31 of a cryorefrigerator, an end portion 33a on the sideof the first cylinder 31 exhibits high temperatures of around 40 K,while a terminal end portion 33b exhibits low temperatures of around 4K. Reference numeral 42 denotes a low temperature end portion to be usedas a cooling head.

In this embodiment, the refrigerating capacity of the second displacer33 is enhanced by optimally changing the regenerative material to befilled in the second displacer 33 serving as the regenerator, dependingon the temperatures of the second displacer 33, so as to make the seconddisplacer 33 more lightweight and compact.

FIG. 2 shows the specific heat characteristics of various regenerativematerials in a cryogenic temperature range of 0-40 K.

Referring to FIG. 2, the regenerative materials differ incharacteristics between a temperature region of 10 K or lower and atemperature region of higher than 10 K. In particular, HoCu₂ exhibits aspecific heat smaller than that of each of Er₃ Co, Er₃ Ni, Ho₂ Al and Pbin the temperature region of greater than 10 K, but exhibits a specificheat greater than that of each of Er₃ Co, Er₃ Ni and Pb in the lowtemperature region of 10 K or lower.

Thus, in this embodiment, as shown in FIG. 1, spherical particles 34 ofHoCu₂ are filled as a regenerative material in a temperature region of10 K or lower (hereinafter, referred to as "final layer") 33c in thesecond displacer 33.

Also, as shown in FIG. 2, in the temperature region of 10 K-15 K, Er₃ Coand Er₃ Ni have specific heats greater than that of each of HoCu₂ andPb. In the temperature region of 15 K or higher, Pb has a specific heatgreater than that of each of Er₃ Co, Er₃ Ni and HoCu₂.

Therefore, as shown in FIG. 1, spherical particles 35 of Er₃ Ni, Er₃ Coor Nd having an equivalent specific heat are filled as a regenerativematerial in the temperature region of 10 K-15 K (hereinafter, referredto as "intermediate layer") 33d in the second displacer 33. Further,spherical particles 36 of Pb are filled as a regenerative material in atemperature region of 15 K or higher (hereinafter, referred to as"initial layer") 33e in the second displacer 33.

As shown above, in this embodiment, the individual temperature regionsof 10 K or lower, 10-15 K, and 15 K or more in the second displacer 33are respectively filled with regenerative materials that exhibit thehighest specific heats for the respective temperature regions. Inparticular, the final layer 33c in which the temperature is 10 K orlower is filled with the spherical particles 34 of HoCu₂ that exhibit aspecific heat greater than that of Er₃ Ni.

Accordingly, as compared with the case where the spherical particles ofEr₃ Ni are filled on the lower temperature side of the second displaceras done in the prior art, the refrigerating capacity of the seconddisplacer 33 is enhanced. Accordingly, the amount of the regenerativematerial to be loaded can be reduced, which makes it possible toconstruct the second displacer 33 in a compact size and in a reducedweight.

As mentioned before, in the case where only one kind of a rare-earthmetal selected among Nd, Er₃ Ni and Er₃ Co is filled in the intermediatelayer 33d of the second displacer 33, temperature fluctuations tend tooccur, as shown in FIG. 3 (indicated by solid line and broken line),during iteration of a refrigerating cycle including introduction andexpansion of the high-pressure refrigerant gas.

Accordingly, in order to prevent such temperature fluctuations in theintermediate layer 33d of the second displacer 33, the regenerativematerial to be filled in the intermediate layer 33d is given by amixture of a plurality of rare-earth metals, as shown in FIGS. 4 and 5.

FIG. 4 is an example of the case where the temperature of ahigh-temperature end portion 41 is as high as 40 K. The final layer 33cand initial layer 33e of the second displacer 33 are filled with thespherical particles 34 of HoCu₂ and the spherical particles 36 of Pb,respectively, like the example shown in FIG. 1. Meanwhile, theintermediate layer 33d is filled with a mixture of spherical particles37 of Pb and spherical particles 38 of Er₃ Ni or Er₃ Co.

FIG. 5 is an example of the case where the temperature of thehigh-temperature end portion 41 is as low as 20 K to 40 K. The finallayer 33c and initial layer 33e of the second displacer 33 are filledwith the spherical particles 34 of HoCu₂ and the spherical particles 36of Pb, respectively, like the example shown in FIG. 1. Meanwhile, theintermediate layer 33d is filled with a mixture of spherical particles39 of Er₃ Co or Ho₂ Al exhibiting specific heat characteristics similarto that of Er₃ Co (see FIG. 2) and spherical particles 40 of Er₃ Ni,HoCu₂, ErNi or an ErNiCo alloy.

The temperature fluctuations that could occur during the repeatedrefrigerating cycles are absorbed by filling the intermediate layer 33dof the second displacer 33 with a regenerative material made of amixture of a plurality of rare-earth metals having more or lessdifferent specific heat characteristics as shown in FIGS. 4 and 5. As aresult, the second displacer 33 can offer a large, stable refrigeratingcapacity.

It is noted here that the mixture of rare-earth metals to be filled inthe intermediate layer 33d of the second displacer 33 is not limited tothose shown in FIG. 4 or FIG. 5. The components of the mixture may beselected appropriately according to the required refrigerating capacityas far as the mixture exhibits a specific heat greater than that ofHoCu₂ filled in the final layer 33c.

The above embodiment has been described for the case where theregenerator of the present invention is implemented by the seconddisplacer of the cryorefrigerator. However, the present invention notbeing limited to this, the regenerator may be implemented by a displacerfor the Stirling refrigerator.

INDUSTRIAL APPLICABILITY

The regenerator of the present invention is used for keeping cryogenictemperatures obtained by iterating the introduction and expansion of ahigh-pressure refrigerant gas, and offers a great refrigeratingcapacity. Further, a small-sized, lightweight cryorefrigerator isrealized by utilizing the regenerator.

We claim:
 1. A regenerator comprising:an initial layer forming a hightemperature region at a temperature higher than 10° C. which is filledwith a regenerative material of Pb or an alloy of Pb; an intermediatelayer forming a first low temperature region at a temperature higherthan 10° K. which is filled with a regenerative material exhibiting aspecific heat greater than that of HoCu₂ and lower than that of Pb in atemperature range corresponding to said intermediate layer; and a finallayer forming a second low temperature region at a temperature of 10° K.or lower which is filled with a regenerative material of HoCu₂.
 2. Theregenerator of claim 1, wherein said intermediate layer is filled with amixture of a plurality of regenerative materials which each exhibit aspecific heat greater than that of HoCu₂ and lower than that of Pb in atemperature range corresponding to said intermediate layer.
 3. Theregenerator of claim 1, wherein said intermediate layer is filled withEr₃ Ni, Er₃ Co or Nd.
 4. The regenerator of claim 2, wherein saidintermediate layer is filled with a mixture of Pb and Er₃ Ni or amixture of Pb and Er₃ Co.
 5. The regenerator of claim 2, wherein saidintermediate layer is filled with a mixture of Er₃ Co or Ho₂ Al, and Er₃Ni, HoCu₂, ErNi, or ErNiCo.
 6. A cryorefrigerator which comprises afirst displacer inserted in a first cylinder and accommodating aregenerative material within a first chamber, and a second displacerinserted in a second cylinder and accommodating a regenerative materialwithin a second chamber, wherein said second displacer is connected tosaid first displacer so that said first chamber communicates with saidsecond chamber, and a refrigerant gas can be introduced from said firstchamber to said second chamber so that heat exchange between therefrigerant gas and the regenerative materials of said first and secondchambers can be carried out,wherein said second chamber contains threelayers comprising a final layer filled with HoCu₂ as a regenerativematerial which forms a second low temperature region of 10° K. or lower;an intermediate layer filled with Er₃ Ni as a regenerative materialwhich forms a first low temperature region of higher than 10° K. and nothigher than a specified temperature; and an initial layer filled with Pbas a regenerative material which forms a high temperature region at atemperature higher than said specified temperature.
 7. Thecryorefrigerator of claim 6, wherein said intermediate layer is filledwith a mixture of a plurality of regenerative materials which eachexhibit a specific heat greater than that of HoCu₂ and lower than thatof Pb in a temperature range corresponding to said intermediate layer.8. The cryorefrigerator of claim 6, wherein said intermediate layer isfilled with Er₃ Ni, Er₃ Co or Nd.
 9. The cryorefrigerator of claim 7,wherein said intermediate layer is filled with a mixture of Pb and Er₃Ni or a mixture of Pb and Er₃ Co.
 10. The cryorefrigerator of claim 7,wherein said intermediate layer is filled with a mixture of Er₃ Co orHO₂ Al, and Er₃ Ni, HoCu₂, ErNi, or ErNiCo.